Review: Humon Hex, optimise training intensity with muscle oxygen

Humon Hex




Ease of use


Use of information





  • Real-time info on muscle oxygen
  • Tells you when to push when to scale back
  • Lets you know when you're adequately warmed up
  • Helps to avoid overtraining
  • Excellent battery life


  • User learning curve
  • It might not be for everyone
  • Collects accurate data on all muscles but strap designed only for use on quads


Hex is a clinically validated wearable that measures muscle oxygen levels. It comes from Boston-based Humon, a company spun out of MIT. The device was originally only available to professional athletes in the US, but since early last year Hex has been made available to all.

Essential readingTop fitness trackers and health gadgets

The gizmo acts as your personal coach. Strap it on to your thigh and you’ll get real-time audio and visual feedback that helps you understand the limits of your body. Hex does this by measuring the hemoglobin saturation in the quadriceps.

Information on muscle oxygen saturation allows you to manage workout intensities in real-time, monitor recovery and muscle fatigue. This essentially provides you with the tools necessary to maximise your effort while avoiding the risk of over-training and potential injury.

I’m an occasional runner who does maybe 3 or 4 runs per week. Did Hex help improve my training? Read on to find out.

Setup and training
Understanding the data
How Hex can help
Mobile app and dashboard


In the box, you’ll find a hexagon shaped pod that houses the smarts, a strap to secure the sensor to your thigh and a charging cable/unit.

This initial product is built for triathletes, runners, cyclists, rowers and skiers. Users are meant to wear it around their thigh, that’s why the strap is pretty large. Humon says they’ve conducted successful experiments using Hex on other muscles. They hope to release new straps/products in the future for different use cases.

The velcro band is comfortable and secures nicely around your quad. This muscle was chosen as typically it is exerted the most during endurance sports. Simply thread the band through the two wings on the sensor. You can then tighten or loosen the hold, as needed.

Humon Hex: optimise training intensity with muscle oxygen

I found on one occasion the pod slipped from my thigh while running which made some of the data unusable. But this was entirely my fault as I did not tighten the strap enough. It only happened once. There is a learning curve involved with Hex, as you’ll find out. This is the case will all new devices, especially ones that are so unique. It’s best to do a few jumps before you start a workout to make sure the hold is firm enough.

Humon Hex: optimise training intensity with muscle oxygenYou can wear Hex under your shorts. As long as it’s in direct contact with the skin and positioned on the working muscle, you are good to go.

The 60.5 x 57 x 13.8mm pod is built of medical-grade plastics and is resistant to sunscreens and lotions – important if you’re running in hot weather. Coming in at 32 grams, it’s also very lightweight.

There’s a single physical button on the front that is used to switch the unit on and off. You can also use this to manually start a recording session. An LED light is right next to it. This blinks red when switched on and not connected, solid red when connected but not recording and green when recording.

If you flip Hex over you’ll notice a row of 5 clear lenses. Behind these is where the magic happens. This is where you’ll find tech that measures oxygen in your muscles via near-infrared spectroscopy. The pod also houses a 64MHz ARM processor.

Humon Hex: optimise training intensity with muscle oxygen

When it comes to water-proofing, the Hex is designed to be IP54 rated. What this means is that it’s resistant to sweat and fine to use in rain. However it is recommended to avoiding showering with the unit on (not sure why anyone would do this…), and don’t even think about submerging it in water. Just clean it once in a while with a damp cloth and it will be fine.

Humon Hex: optimise training intensity with muscle oxygenThe device has both Bluetooth and ANT+ compatibility. This means you can record your workout on a smartphone (using BLE) and, at the same time, see the data on a Garmin watch (using ANT+). You can also pair Hex with bluetooth heart rate monitors (but not ANT+ heart rate monitors at this time).

Battery life is pretty good. The gizmo will keep going for around 20 hours between charges which is more than enough for a couple of weeks of training for most people. Charging is done via a QI wireless charger which works very well.

You’ll know when the device is fully topped up by keeping an eye on the LED light. About an hour is how long it takes to go from empty to full.

Setup and training

To start using Hex you’ll need to download the accompanying iOS or Android app, install it on your smartphone and create a profile by answering a few basic questions. All this takes only a few minutes.

As mentioned, you can also use Hex with a Garmin watch that supports Connect IQ. This includes most of the devices in the Forerunner series, the Fenix range, Vivoactive 3 and more. My watch of choice is the Forerunner 935, something to keep in mind when reading this review.

Humon Hex: optimise training intensity with muscle oxygen

If you wish to use Hex with a Garmin device, you’ll need to download the Humon Garmin Data Field and install it on your watch. This is done via Garmin Express. There are two fields you can download, one for endurance training and the other one for intervals. Which of the two you’ll use depends on the type of training session.

Connecting Hex to a watch makes it much more valuable as a training assistant. After some experimenting, I found that it’s actually best to connect Hex to both the mobile app and Garmin watch at the same time. Each has its distinct benefits in terms of information provided. Having said that, you can train with just the smartphone app or just a Garmin watch.

To start a session, you’ll first need to pair Hex (and optionally a heart rate chest strap) to the smartphone via the app (using BLE). I would typically do this before I start my warmup. The next step is selecting the Activity and Type. Activity allows you to choose between running, cycling, rowing and other. Type consists of interval training, endurance and threshold test. Then tap on Start Workout with Hex strapped to your thigh. It will take about 15-20 seconds to calibrate.

Humon Hex: hack into your muscle oxygen levels to improve trainingWhen you’ve warmed up enough and are ready to begin your run or cycle, you can start recording your workout with the Garmin device using ANT+. This will give you access to real time muscle oxygen data on both the watch and the smartphone app.

The Garmin display shows your SmO2 percentage and, following a recent update, it is also colour-coded. The latter is particularly useful as it allows you to know at a glance which zone you are currently in. The Humon smartphone app has the added benefit of showing a real-time incremental graph on how your SmO2 is changing.

It’s worth pointing out, the sensor should not be paired to the watch using Garmin’s native pairing system, a mistake I made early on. If you’ve done this, you’ll need to unpair it. The Hex has been designed to start broadcasting data when switched on and the Garmin watch will automatically pick up the signal and display the values if you’ve added the Data Field.

Another alternative is to just start recording without using the mobile app. This can be done by double-clicking the physical button on the sensor. But you’ll find that there is lots of value in letting the smartphone track the warmup and recovery period of your workout. You probably do not want to track these with your Garmin watch as there is little value in doing so.

Understanding the data

First for the science lesson. Oxygen is fuel needed by muscles for energy. By elevating the heart rate, the body is able to increase blood flow to the muscles and deliver more oxygen.

Humon Hex: optimise training intensity with muscle oxygen

We’ve written before about aerobic and anaerobic training. With aerobic training, oxygen from breathing is filtered down to the muscles to give them energy. This is done via red blood cells which bind oxygen to a protein in the cell called hemoglobin (HbO2).

With anaerobic training, the body’s demand for oxygen exceeds the supply available through breathing. This is when the hemoglobin becomes deoxygenated (Hb). At this point glycogen (sugar) is also used by muscles as fuel. This causes a buildup of lactic acid in your body which causes discomfort and fatigue. Such effort is unsustainable and you’re going hit the wall in terms of performance pretty quickly.

This point is also called the lactate threshold. It is one of the most used metrics in the world of training by athletes and coaches worldwide. Both aerobic and anaerobic training have their own benefits.

In a nutshell, Hex measures the concentrations of oxygen-hemoglobin (HbO2) and deoxy-hemoglobin (Hb) in your muscle. The SmO2 is then derived by calculating the ratio of HbO2 to the total hemoglobin (HbO2 + Hb).

Monitoring SmO2 is perhaps the best physiological indicator of an athlete’s exertion. This type of measurement provides the benefits of both VO2max and lactate threshold testing as it measures the balance between the supply and demand of oxygen to the muscles during exercise.

But don’t confuse muscle oxygen with blood oxygen (SpO2) as the two are vastly different. SpO2 measures oxygen supply, while SmO2 captures utilisation.

Typical values for SpO2 fall between 95-99%. Unless you’re climbing a mountain or flying an airplane, this metric is informative as a general health assessment but less valuable in training situations. SmO2, on the other hand, gives an indication of the balance between oxygen delivery and consumption in the muscles.

Humon Hex: optimise training intensity with muscle oxygen

How Hex can help

With the science lesson out of the way, it becomes clearer how Hex can help. The gizmo shines a light in the near-infrared wavelength range to penetrate your quad muscle. By determining how this light is absorbed, it is able to quantify the concentrations of oxygen in hemoglobin.

Knowing this information has many benefits. For example, it allows you to warm-up properly and lets you know when you’ve sufficiently recovered for a new training session. Even more importantly, it gives you precise real-time information on the state of your muscles. Understanding how hard you are pushing at any given point allows you to optimise your effort as you are exercising.

Plus you can be confident in the data. Hex has been found in a clinical trial (by Harvard Medical School) to be 96% accurate when compared to the gold-standard bench top tissue oximeter.

Humon Hex: optimise training intensity with muscle oxygen
Example of a steady state 5K run (including warmup and recovery)

The Hex classifies the muscle as being in one of four zones. It is important to understand each of them.

1) Increasing SmO2 means the delivery of oxygen to the muscles is greater than consumption. You are engaged in low intensity activity (including a recovery or a warmup), as as indicated by the blue “recovery” zone.

2) Steady SmO2 means a balance has been struck. This is an effort that you can sustain for a long time. Think long slow bike riding or running. Hex calls this the green ‘steady state’ zone.

3 & 4) Finally, decreasing SmO2 means oxygen is being consumed faster than it is being supplied. This occurs when you are pushing yourself, for example during High-Intensity-Interval-Training (HIIT) or a sprint. This is indicated by the orange and red zones. The first is a warning you are approaching your body’s limit, the second that you are going at an unsustainable pace.

Simply by keeping an eye on the change in SmO2 values on your watch or smartphone (as indicated by the colour), you are now able to pace yourself. For example, during my endurance training I would make sure I was in the green/blue zones. It was only towards the end of the session that I would push towards the orange/red zones.

If you are doing HIIT, you now have a precise way of identifying how long and hard to push during each interval. Hex also also provides better data on readiness for the next effort than just heart rate or elapsed time.

For example, by using the device I found that I wasn’t pushing hard enough when doing HIIT, i.e. at times I wasn’t hitting the orange/red zones. A useful lesson that made my future sessions much more productive. Another time I found that I was feeling the effects of training from the previous day, which made it impossible to reach the orange/red zones during HIIT. So I reverted to an easy steady-state run that day.

Humon Hex: optimise training intensity with muscle oxygen
HIIT session (including warmup and recovery)

The gizmo also lets you know when you are sufficiently warmed up. Does it take 5 minutes, 15 minutes? Hard to tell. The answer depends on a variety of factors such as your fitness level, the temperature of the environment and more.

Humon Hex: optimise training intensity with muscle oxygen
Overlay of MuscleOx data with and without a warm up | Source: Humon

At the start of an exercise your muscle oxygen will typically decline drastically. After a few minutes it will start to recover as it receives more oxygen that it is using. When it plateaus, the warmup is finished. Hex allows you to identify this point.

The above screenshot is an example of a HIIT session where I had not warmed up enough. Instead of going longer to give my muscles a chance to oxygenate properly, I pushed for the first interval way too soon. This made the training session less effective as I hit the orange and red zones pretty quickly. Had I allowed myself more time to warm up, I would have been able to push harder during the intervals.

The image on the right comes from Humon. It shows an overlay of SmO2 data of a cyclist. The difference in performance between the sessions (one with and the other without a proper warmup) is drastic.

Finally, information on the recovery stage is also useful. Hex is able to look at how your muscles are recuperating immediately after the exercise (as long as you keep it switched on) and let you know what’s going on.

Put simply (although I am sure there is more to it), a good recovery will go through a blue stage which will soon be followed by a green “steady state” stage. If you find that your muscle is in the blue stage far longer than usual, it might be time to rest.

Luckily, the analysis is done for you. After each workout the app will spit out a ‘Tip’. On one occasion it told me that: “The intensity was good but your muscles did not recover well. This is a sign of fatigue and it might be time for a day off”. It couldn’t have been more right as I was absolutely exhausted the following day! It also made me feel less guilty on taking that rest day.

Humon Hex: optimise training intensity with muscle oxygen

But don’t put too much stock into variations of your SmO2 values from day to day. This changes depending on the state of your muscles. I suspect it also depends on how exactly you position the device. The value of the metric is not so much the metric itself, but how it fluctuates during exercise.

Nevertheless, Humon has calculated that the average SmO2 is 64% (± 10%), maximum 72% (± 10%) and minimum 52 (± 17%). I found myself to be well within these ranges most days.

Mobile app and dashboard

Humon Hex: optimise training intensity with muscle oxygenThe app consists of four tabs: Workout, History, Profile and Settings.

Workout is used to pair your Hex and HRM (optionally). This is where you choose the type of workout and start a session.

History shows a timeline of your activity. Tap on any session to access detailed data including average pace, distance, duration, a map and zone distribution.

You are also awarded a score after each session on how optimised your workout was. Anything below 75 suggests less than optimal, above 100 indicates highly optimised. The effort level ranges between 1 and 4. This represents the overall intensity of the workout.

You’ll then see a graph on how you muscle oxygen has changed during the session, as well as minimum, average and splits. If you’ve connected a HRM you’ll see underneath a chart on how your heart rate has changed during the session.

The Profile page shows a running total of your workouts. You’ll find information on the number of workouts, total time, how you compare with others and more.

Humon Hex: optimise training intensity with muscle oxygen

In addition to the smartphone app, you can also access a web dashboard. This allows you to see pretty much all of this data but in more detail – such as a chart on hemoglobin concentration in your muscles. You can also export your workout data in CSV, JSON, TCX and GPX file formats for importing into Training Peaks, Strava and other platforms.

If you’ve connected a Garmin watch to Hex, Garmin Connect will show data collected using the Humon Data Field. But rather than SmO2, you’ll get charts on hemoglobin concentration in the blood and hemoglobin percentage. Which makes this of limited use.

Garmin requires that Hex data/units give concentration in the blood rather than what the thing really measures (in the muscle). Humon says what’s more important when looking at this hemoglobin concentration data is the directional change during a workout.

A direct connection between the Humon app and Garmin Connect does not exist at the moment. Perhaps something that will be upgraded via a future firmware update. However, a FIT file import feature does exist to accommodate Garmin users who don’t want to carry their smartphone during exercise. This allows them to export all of their data into the Humon environment and receive detailed post workout muscle oxygen feedback.

This review wouldn’t be complete without touching on the Hex threshold test. This is done via a treadmill or a stationary bike and it takes about a half an hour to complete.

The running threshold test is still in beta stage. You start off on a treadmill at a very slow pace for 3 minutes. Increase the speed by 1 km/h every 3 minutes until you reach exhaustion. For cycling the test is done by starting off at a very low power (30W) for 3 minutes. You then increase the wattage by 30W every 3 minutes. Keep doing this until you absolutely can’t push any further.

Hex estimated my threshold for running at 10.4 km per hour and 193 watts for cycling.

Humon Hex: optimise training intensity with muscle oxygen

These tests should be done at regular intervals to check on progress and tweak heart rate and power training zones. Measuring your lactate threshold using Hex could also be a great alternative for those paying upwards of $100 for professional lab tests.


The verdict

I wanted to like Hex as it piqued my interest when I first heard about it a few years back. Ultimately, I ended up loving it.

I am by no means a hard-core runner, clocking (on a good week) perhaps 15 kilometres. Nevertheless Hex has been surprisingly useful. Over the years I’ve tested lots of fitness gadgets, but this is probably the one that has taught me the most about the workings of my body.

I now understand the value of an adequate warmup and how it effects performance, how to do interval training properly and when it might be time to scale back and take a well earned rest day. With Hex I could adjust my effort accordingly. It takes guesswork out of the equation.

Humon Hex: become your own coach with muscle oxygen sensor for
Humon Hex
Gadgets & Wearables may get a commission
Review: Humon Hex, optimise training intensity with muscle oxygen

It’s worth noting, there is a user learning curve. In reality, it will probably take you a week or two to get to grips with all the nuances of the product. But once that’s out of the way, everything will run smoothly and you’ll get instant feedback on the state of your muscles. Not just during exercise but also in warmup and recovery.

The band is extremely comfortable, wireless charging is flawless and the battery life is great. If you’re an endurance athlete or even a newbie, I definitely would suggest giving muscle oxygen training a try.

At the moment Hex is the only such affordable option on the market. I can definitely see it becoming a bigger part of my exercise routine, and look forward to future updates.

We are a review site that receives a small commission from sales of certain items, but the price is the same for you. Purchasing items by clicking on links in this article allows us to run this website. We are independently owned and all opinions expressed here are our own. See our affiliate disclosure page for more details.

Like this article? Subscribe to our monthly newsletter and never miss out!

Marko Maslakovic

Marko founded Gadgets & Wearables in 2014, having worked for more than 15 years in the City of London’s financial district. Since then, he has led the company’s charge to become a leading information source on health and fitness gadgets and wearables.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.